Methylphenidate is a psychostimulant which is a chain substituted amphetamine derivative. Similar to amphetamine and cocaine, methylphenidate targets the central nervous system, specifically the dopamine transporter (DAT) and norepinephrine transporter (NET). Methylphenidate is thought to act by increasing the concentrations of dopamine and norepinephrine in the synaptic cleft, as methylphenidate has both dopamine transporter (DAT) and norepinephrine transporter (NET) binding capabilities. Although an amphetamine derivative, the pharmacology of methylphenidate and amphetamine differ, as amphetamine is a dopamine transport substrate whereas methylphenidate works as a dopamine transport blocker. As a norepinephrine and dopamine re-uptake inhibitor, methylphenidate thus blocks re-uptake of dopamine and norepinephrine (noradrenaline) into presynaptic neurons (and possibly stimulates the release of dopamine from dopamine nerve terminals at high doses), thereby increasing the levels of dopamine and norepinephrine in the synapse. In some in vitro studies, methylphenidate has been shown to be more potent as an inhibitor of norepinephrine uptake/re-uptake when compared to dopamine. However, some in vivo studies have indicated that methylphenidate is more potent in potentiating extracellular dopamine concentrations than norepinephrine concentrations. Unlike amphetamine, it has been duggested in the scientific and/or clinical research community that methylphenidate does not seem to significantly facilitate the release of these two monoamine neurotransmitters at therapeutic doses.
Four isomers of methylphenidate are known to exist: d-erythro-methylphenidate, l-erythro-methylphenidate, d-threo-methylphenidate, and l-threo-methylphenidate. Originally, methylphenidate was marketed as a mixture of two racemates, d/l-erythro-methylphenidate and d/l-threo-methylphenidate. Subsequent research showed that most of the pharmacological activity of the mixture is associated with the threo-isomer resulting in the marketing of the isolated threo-methylphenidate racemate. Later, the scientific community determined that the d-threo-isomer is mostly responsible for the stimulant activity. Consequently, new products were developed containing only d-threo-methylphenidate (also known as “d-threo-MPH”).
Stimulants, including methylphenidate (“MPH”), are believed to enhance the activity of the sympathetic nervous system and/or central nervous system (CNS). Stimulants such as MPH and the various forms and derivatives thereof are used for the treatment of a range of conditions and disorders predominantly encompassing, for example, attention deficit hyperactivity disorder (ADHD), attention deficit disorder (ADD), obesity, narcolepsy, appetite suppression, depression, anxiety and/or wakefulness.
Methylphenidate is currently approved by the United States Food and Drug Administration (“FDA”) for the treatment of attention-deficit hyperactivity disorder and narcolepsy. Methylphenidate has also shown efficacy for some off-label indications that include depression, obesity and lethargy. In some embodiments, the prodrugs of the present technology may be administered for the treatment of attention-deficit hyperactivity disorder and narcolepsy, or any condition that requires the blocking of the norepinephrine and/or dopamine transporters.
Attention deficit hyperactivity disorder (ADHD) in children has been treated with stimulants for many years. However, more recently, an increase in the number of prescriptions for ADHD therapy in the adult population has, at times, outperformed the growth of the pediatric market. Although there are various drugs currently in use for the treatment of ADHD, including some stimulants and some non-stimulant drugs, methylphenidate (commercially available from, for example, Novartis International AG (located in Basel, Switzerland) under the trademark Ritalin®) is commonly prescribed. Moreover, during classroom trials, non-stimulants have shown to be less effective in improving behavior and attention of ADHD afflicted children than amphetamine derivatives.
Behavioral deterioration (rebound or “crashing”) is observed in a significant portion of children with ADHD as the medication wears off, typically in the afternoon or early evening. Rebound symptoms include, for example, irritability, crankiness, hyperactivity worse than in the unmedicated state, sadness, crying, and in rare cases psychotic episodes. The symptoms may subside quickly or last several hours. Some patients may experience rebound/crashing so severe that treatment must be discontinued. Rebound/crashing effects can also give rise to addictive behavior by enticing patients to administer additional doses of stimulant with the intent to prevent anticipated rebound/crashing negative outcomes and side effects.
Stimulants, such as methylphenidate and amphetamine, have been shown in the conventional art to exhibit noradrenergic and dopaminergic effects that can lead to cardiovascular events comprising, for example, increased heart rate, hypertension, palpitations, tachycardia and in isolated cases cardiomyopathy, stroke, myocardial infarction and/or sudden death. Consequently, currently available stimulants expose patients with pre-existing structural cardiac abnormalities or other severe cardiac indications to even greater health risks and are frequently not used or used with caution in this patient population.
Methylphenidate, like other stimulants and amphetamine derivatives, can become addictive and is prone to substance abuse. Oral abuse has been reported, and euphoria can be achieved through intranasal and intravenous administration.
Methylphenidate also has limited water solubility especially in an unconjugated form. The properties of limited bioavailability and limited water solubility make formulating methylphenidate for oral administration more difficult because the dosage forms for administration are limited. There is a need in the art for more bioavailable and water soluble forms of methylphenidate that maintain the pharmacological benefit when administered, in particular via the oral route.